src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -117,8 +117,11 @@ public class DotsAndBoxesGrid {
 
         // A box is complete if the north and south horizontals and the east and west verticals have all been drawn.
         // FIXME: You'll need to fix this code (after writing a test first).
+        if ((getHorizontal(x, y) && getHorizontal(x, y + 1)) && (getVertical(x, y) && getVertical(x + 1, y))) {
             return true;
         }
+        return false;
+    }
 
     /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
     private boolean claimBox(int x, int y, int p) {
@@ -147,6 +150,9 @@ public class DotsAndBoxesGrid {
         }
 
         // FIXME: You need to throw an exception if the line was already drawn.
+        if (getHorizontal(x, y)) {
+            throw new IllegalArgumentException(String.format("line at coordinate (%d, %d) already exists. Try other coordinates", x, y));
+        }
 
         this.horizontals[x][y] = true; // otherwise set the horizontal line to true
 
@@ -179,6 +185,9 @@ public class DotsAndBoxesGrid {
         
         // FIX this too, whether vertical line was already drawn or not
         // You need to throw an exception if the line was already drawn.
+        if (getVertical(x, y)) {
+            throw new IllegalArgumentException(String.format("line at coordinate (%d, %d) already exists. Try other coordinates", x, y));
+        }
 
         this.verticals[x][y] = true; // otherwise set the vertical line to true